The present invention relates to a stationary dredging apparatus for automatically removing sand and silt from waterways, and more particularly, to means for cleaning out the dredge and removing any sedimentary deposits and objects that have clogged the perforations or openings along the dredge thereby blocking the fluid stream in the dredge.
In U.S. Pat. No. 3,638,432 which issued to the present applicant, a stationary dredge is disclosed in which a generally horizontal pipe is laid on the bottom of the waterway which is connected to the suction line of the pump. The horizontal line is provided with a plurality of perforations or openings into which sand and silt are drawn by the suction of the pump. Clear water, that is water that is clear of sand and silt, is supplied to the horizontal line near the perforations closest to the connection to the pump to dilute the slurry passing through the perforated pipe and thereby reduce clogging. One disadvantage of this system is that when used in areas having high kelp growth or where a large amount of non-granular debris such as cans, bottles or water-logged driftwood for example, have settled on the bottom these non-granular debris are drawn by suction over the perforations thereby clogging them. This same disadvantage also pertains to other types of silt removing perforated lines which rest on the bottom of a waterway.
U.S. Ser. No. 427,077, the parent to the present case, provides for a self-cleaning stationary conduit for removing sand and silt materials from the conduit which comprises a plurality of nozzles which provide a high velocity of water jets into a plurality of orifices along the stationary pipeline. The high velocity jets of water mix with the bottom sand near the stationary conduit to degrade any solid material which tends to block the orifices of the conduit. The invention as disclosed in the parent application will clear the orifice opening of any debris build-up where the debris consists of small objects or deposits of sediment, but it is still possible for a passageway to be blocked by a large object. Thus, the high velocity of water jets emanating from the nozzles may only serve to puncture a hole in one side of some very large object without removing the entire object. It therefore follows that some means for manually removing large objects, such as tires, from above or about the orifice openings is desirable.
The problem of removing the obstructing object is not serious because on the rare occasions when such an obstruction occurs, a diver can be sent down to clear it. The real problem, however, is how to get to the obstruction. Typically, the passageways into the dredging pipe may be ten feet apart and the dredging pipe may be thirty (30) feet below the surface of the sand when dredging starts. Thus, the obstruction at one passageway may be under the center of a pile of sand twenty feet long, or more, and six (6) or more feet high. The pile of sand problem would not be so great if the passageways into the pipe were closer together, but the pipe can have only a limited number of passageways of a given size for a given pump size so that making the passageways closer together would require that the pipe be shorter and hence less effective in maintaining a large dredged area.